1. Field of the Invention
The present invention generally relates to an image forming apparatus and an image forming method of effectively detecting a speed deviation pattern of the image forming apparatus, and more particularly relates to an image forming apparatus that can effectively detect a speed deviation pattern of an image bearing member included in the image forming apparatus with high accuracy, and an image forming method of effectively detecting the speed deviation pattern of the image forming apparatus.
2. Discussion of the Related Art
An image forming apparatus using electrophotography may include a plurality of image bearing members such as photoconductors, and a transfer member (e.g., transfer belt) that may be disposed facing the image bearing members. The transfer member may travel in an endless manner in one direction.
In such image forming apparatus, toner images having different color may be formed on each of the image bearing members.
Such toner images may be superimposingly transferred directly onto a recording medium (e.g., transfer sheet) that is conveyed on and by a transfer member. By performing the above-described action, a full-color toner image may be formed on the recording medium. This is a direct transfer method.
Instead of the above-described direct transfer method, an indirect transfer method may also be used.
In the indirect transfer method, toner images may be superimposingly transferred onto the transfer member, then transferred onto a recording medium to form a full-color toner image thereon.
In such configuration, sometimes, toner images may not be correctly superimposed on the recording medium by several factors. Such factors may include an eccentricity of a photoconductor serving as an image bearing member, an eccentricity of a drive-force transmitting member (e.g., a photoconductor gear) that concentrically rotates with the photoconductor, and an eccentricity of a coupling that is connected to the photoconductor, for example.
Specifically, if the photoconductor or the drive-force transmitting member may have an eccentricity, the photoconductor may have two areas (e.g., first and second areas) on a surface of photoconductor with respect to a diameter direction of the photoconductor.
For example, the first area of the photoconductor may rotate with a relatively faster speed due to the eccentricity, and the second area of the photoconductor may rotate with a relatively slower speed due to the eccentricity, wherein such first and second areas may be distanced from each other by 180 degrees with respect to a diameter direction of the photoconductor, for example.
In such a case, first image dots formed on the first area of the surface of the photoconductor may be transferred to a transfer member at a timing earlier than an optimal timing, and second image dots formed on the second area of the surface of the photoconductor may be transferred to the transfer member at a timing later than an optimal timing.
If such phenomenon may occur, the first image dots formed on a surface of a photoconductor may be superimposed on the second image dots formed on a surface of a different photoconductor. Similarly, the second image dots formed on a surface of a photoconductor may be superimposed with the first image dots formed on a surface of a different photoconductor.
Such phenomenon may cause incorrect superimposing of toner images having different colors.
In another image forming apparatus, a controller may conduct a speed deviation checking and a phase adjustment control for toner images to reduce an incorrect superimposing of toner images.
The speed deviation checking may be conducted by detecting a deviation of a surface speed of an image bearing member (e.g., a photoconductor) when conducting an image forming operation.
The phase adjustment control may be conducted by adjusting a phase of each image bearing member based on the speed deviation checking.
In a case in which the speed deviation checking is conducted, a plurality of toner images may be formed with a given pitch from each other on a surface of an image bearing member in a surface moving direction of the image bearing member.
Such plurality of toner images may be then transferred onto a transfer member (e.g., a transfer belt) as a pattern image, and a photosensor may detect each of the toner images included in the pattern image.
Based on a detection result by the photosensor, a pitch of toner images included in the pattern image may be computed.
Based on the computed pitch, a speed deviation per one revolution of each of the image bearing members may be determined.
Furthermore, another photosensor may detect a marking placed on a photoconductor gear, which rotates the image bearing member, to detect a timing when the image bearing member comes to a given rotational angle.
With such process, the controller of the image forming apparatus may compute a difference between a first timing when the image bearing member comes to the given rotational angle and a second timing when the surface speed of the image bearing member becomes a maximum or minimum speed.
Such process may be conducted for each of the image bearing members.
After such speed deviation checking has been conducted, a phase adjustment control may be conducted to adjust a phase of image bearing members.
Specifically, a photosensor may detect a marking placed on a given position of a photoconductor gear, which rotates with a photoconductor serving as an image bearing member.
A plurality of photosensors may be used to detect a marking placed on a given position of photoconductor gears, which rotates respective photoconductors.
With such process, a timing when each of the photoconductors becomes a given rotational angle may be detected.
Based on such information including rotational angle and speed deviation of the respective photoconductors, a plurality of drive motors, which respectively drive each of the photoconductors, are driven by changing a driving time period temporarily to adjust a phase of the photoconductors.
With such phase adjustment of photoconductors, image dots that may come to a transfer position at an earlier timing than an optimal timing, or image dots that may come to a transfer position at a later timing than an optimal timing, may come to a transfer position at an optimal timing.
With such controlling, a superimposing deviation of images may be reduced.
In an image forming apparatus having such configuration, a speed deviation pattern of a photoconductor due to an eccentricity of the photoconductor may be detected.
For detecting such speed deviation pattern with high accuracy, however, the photoconductor of the image forming apparatus may need to be rotated for several times to detect the speed deviation of the photoconductor, so that a speed deviation component due to a factor different from an eccentricity of the photoconductor may be removed.
Hereinafter, a speed deviation component due to a factor different from an eccentricity of a photoconductor will be referred to as a “speed deviation component independent from a photoconductor.”
The speed deviation component independent from a photoconductor may include a component of belt speed deviation due to an eccentricity of a drive roller that may drive an intermediate transfer belt, for example.
A speed deviation checking pattern image that can be extendedly formed over a surface of a photoconductor for several revolutions of the photoconductor may be formed and detected.
However, patch toner images of the speed deviation checking pattern image may be formed at a relatively different position for each revolution or rotation cycle of the photoconductor. That is, the patch toner images may have a relative positional deviation for each revolution or rotation cycle of the photoconductor.
Specifically, a patch toner image in a speed deviation checking pattern image may need to be formed at design pitches or pitches that may be set according to a resolution of the image forming apparatus.
For example, when an image forming apparatus has a resolution of 600 dpi, a dot formation pitch between patch toner images may be approximately 42 μm. Accordingly, the pitch for forming the patch toner images may be obtained by multiplying the dot formation pitch of approximately 42 μm with an integer number (e.g., one, two, three).
Then, each patch toner image may be formed at a time interval corresponding to the pitch to detect a speed deviation pattern based on a pitch deviation of an actually formed patch toner image of the speed deviation checking pattern image.
In general, however, the pitch of patch toner images may not be equal to a value obtained by multiplying a circumferential length of a photoconductor with an integer number (e.g., one, two, three). Therefore, the circumferential length of the photoconductor cannot be divided by the pitch of patch toner images.
For example, a speed deviation checking pattern image that can be extendedly formed over a surface of a photoconductor for several revolutions of the photoconductor may be formed against the above-described fact.
If a first patch toner image for a first revolution of the photoconductor is formed at a given position on the photoconductor, a first patch toner image for a second revolution of the photoconductor may be formed at a different position slightly apart from the given position.
Each first patch toner image for respective revolutions after the second revolution of the photoconductor may be formed at a different position slightly away from the position at which the first patch toner image for the previous revolution is formed.
When such positional deviation of patch toner images occurs, speed data based on a detection timing of each patch toner image for each revolution of the photoconductor may not synchronize with each other.
It is known to conduct synchronous addition processing to remove a speed deviation component of an image forming unit independent from the photoconductor. However, to remove such a speed deviation component, speed data for each revolution of the photoconductor may need to be corrected to synchronize with each other.
This, however, may cause complex arithmetic processing for synchronizing speed data of each revolution of the photoconductor.
To avoid such complex arithmetic processing, when the photoconductor comes to a given rotational angle of each revolution, speed data for each revolution may be synchronized with each other and a first patch toner image for each revolution may be formed at the same position.
In this case, an expensive and highly responsive detecting unit detecting the above-described rotational angle may be required. Otherwise, a positional deviation of a patch toner image caused by response speed deviation of the above-described detecting unit for each revolution may occur.
Accordingly, it may become difficult to detect a speed deviation checking pattern image with desired accuracy.